Various types of sensors have been employed for monitoring document handling in imaging apparatus such as scanners, copiers, printers, fax machines, and other equipment that obtains data from, or imprint images and text onto, paper or other sheet media. Automatic document feed systems have used a range of different types of mechanical, optical, and audio sensors for this purpose.
Document feeding stations are particularly prone to problems caused by staples, paperclips, adhesives and other fasteners, poor document preparation or stacking, folds or wrinkles in the fed media sheet, different media weights and thicknesses, and other media-related problems, as well as problems with the media transport components themselves, caused by wear, dust and dirt, and other factors. These problems can be particularly acute with high-speed scanning systems or with scanners that handle financial and other business documents. Failure to detect a jam or other misfeed condition in time can damage the original document, cause loss of data, require special handling to correct the problem, and reduce equipment efficiency due to down time.
With no moving parts, requiring no contact with the moving media, and because they are less susceptible to problems caused by dirt or other particulates, audio sensors have some advantages for use along the media transport path. Audio sensors can perform acceptably when used in place of electrical or optical sensors. However, with conventional solutions in deployment of audio sensors, many of the same problems in document feeding and handling persist.
Thus, it can be seen that there is a need for improved apparatus and methods for detecting document feed problems and helping to prevent damage to documents due to misfeeds and jams.